The present invention relates to a computer system and a method of controlling the rotation speed of a cooling fan, and particularly, to a method for controlling a cooling fan applied to a computer system including a CPU having a power save mode.
In recent personal computer systems of a laptop or notebook type, it is necessary to reduce not only the temperature of the CPU but also the surface temperature of the casing. In particular, it is necessary to reduce an increase of the surface temperature of the casing due to heat generation from the power source circuit. Also, rotation of a cooling fan results in a shorter battery life and unwanted noise. Therefore, it is required to put the fan not rotated as much as possible and to lower the rotation speed of the fan as much as possible (per unit time). Therefore, it is desirable to efficiently cool the CPU and power source circuit using a cooling fan.
Meanwhile, the element in a computer system, which generates most heat, is the CPU. Therefore, a cooling module which integrates a heat sink and a fan together is installed on the CPU, and ON/OFF control or rotation speed control of the fan is carried out in accordance with the detection value (temperature) of a temperature sensor included in the CPU. In this case, ventilation of the power source circuit is carried out at the same time the fan is rotated. Thus, the module also serves to cool the power source circuit. Control is performed only on the basis of the temperature of the CPU because it is supported that “the temperature of the power source circuit is high when the temperature of the CPU is high, and the temperature of the power source circuit is low when the temperature of the CPU is low”.
In recent years, INTEL's SpeedStep™ power-saving technology has adopted in CPUs. This CPU automatically switches to a power save mode using a low voltage and a low CPU clock frequency from a normal mode using a high voltage and a high CPU clock frequency during operation. In the power save mode, the power consumption of the CPU is reduced so that the heat generation of the CPU can be restricted. However, in view of the entire power source circuit, heat generation of the power source circuit is left substantially unchanged because power consumption of the other units does not change. Hence, the conventional supposition that “the temperature of the power source circuit is low when the temperature of the CPU is low” is not satisfied. There appears a situation in which “the temperature of the power source circuit is high even when the temperature of the CPU is low”. Therefore, there may be a case where the power source circuit has an unexpectedly high temperature with control based only on the temperature of the CPU. Peripheral circuits hence may be damaged.